This invention is generally directed to layered photoresponsive imaging members comprised of novel electron transporting compounds and more specifically, the present invention is directed to sulfur incorporated dicyanomethylenefluorene carboxylates which can be selected for use in layered photoresponsive imaging members as electron transporting substances. Accordingly, in one specific embodiment of the present invention there is provided a layered photoresponsive imaging member, or device with a photogenerating layer, and in contact therewith an electron transporting substance comprised of sulfur incorporated dicyanomethylenefluorene carboxylates dispersed in an inactive resinous binder material. In one alternative embodiment of the present invention there is provided a layered photoresponsive device wherein the electron transporting compositions selected have added thereto, or are doped with various effective stabilizers, inclusive of aromatic diamines as illustrated herein. Imaging members having incorporated therein the novel organic sulfur compositions of the present invention as electron transporting substances are useful in many imaging systems, particularly electrostatographic imaging systems wherein the member is initially charged positively thereby enabling the use of such a member for generating colored images and wherein known negatively charged developer compositions can be selected, thereby desirably, in some instances, eliminating the need for charge enhancing additives.
The use of electron transporting substances in photoresponsive imaging members is disclosed in a copending application U.S. Ser. No. 521,198, entitled Layered Photoresponsive Device, the disclosure of which is totally incorporated herein by reference. In this application, there is described an improved photoresponsive imaging member comprised of a supporting substrate, a photogenerating layer, and in contact with the photogenerating layer, an electron transporting layer comprised of novel fluorenylidenemethane compositions. While these compositions are suitable for the intended purposes, there is a need for other electron transporting materials especially those which are relatively stable in resinous binders, and thus do not crystallize; and further wherein the resulting imaging member has improved cycle-up, and cycle-down characteristics.
Also, the formation and development of electrostatic latent images on the imaging surfaces of photoconductive materials by electrostatic means is well known. The photoreceptor selected is generally comprised of a conductive substrate containing on its surface a layer of photoconductive material, and in many instances a thin barrier layer is situated between the substrate and the photoconductive layer to prevent charge injection from the substrate, which injection could adversely affect the quality of the images generated.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material, such as vitreous selenium, or a composite layered device with a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described, for example, in U.S. Pat. No. 3,121,006 wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resinous binder. In a commercial form the binder layer comprises particles of zinc oxide uniformly dispersed in a resinous binder, and coated on a paper backing. The binder material as disclosed in this patent comprises a composition which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Illustrative examples of specific binder materials include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
There are also known photoreceptor compositions comprised of inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performance standards, and to obtain high quality color images. Additionally, layered photoresponsive devices are desired which can be charged positively, and contain therein an electron transporting material.
Recently, there have been disclosed layered photoresponsive members comprised of photogenerating layers, and transport layers, as described in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials with a hole injecting layer, in contact with a transport layer, an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, reference, for example, U.S. Pat. No. 4,251,612. Examples of generating layers disclosed in these patents include trigonal selenium, and phthalocyanines, while examples of transport layers that may be used, which layers transport positive charges, in contrast to the transport layers of the present invention, which transport electrons include certain diamines dispersed in a resinous binder. The disclosure of each of these patents, namely U.S. Pat. Nos. 4,265,990 and 4,251,612, are totally incorporated herein by reference.
Many other patents are in existence describing photoresponsive imaging members including those with photogenerating substances, such as U.S. Pat. No. 3,041,167, which discloses an overcoated imaging member comprised of a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in electrophotographic copying by, for example, initially charging the member with electrostatic charges of a first polarity, and imagewise exposing to form an electrostatic latent image, which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second polarity which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied creating across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer by applying an electrical potential to the conductive substrate. The imaging potential which is developed to form the visible image is present across the photoconductive layer, and the overcoating layer.
Furthermore, there is disclosed in U.S. Pat. No. 4,135,928 electrophotographic light sensitive members with 7-nitro-2-aza-9-fluorenylidene-malononitrile as a charge transporting substance. According to the disclosure of this patent, the electrophotographic light sensitive members comprise an electroconductive support, a layer thereof comprising a charge generating substance, and 7-nitro-2-aza-9-fluorenylidene-malononitrile, of the formula, for example, as illustrated in column 1.
Other representative patents disclosing layered photoresponsive imaging members include U.S. Pat. Nos. 4,115,116, 4,047,949, and 4,315,981. There is disclosed in the '981 patent an electrophotographic recording member with an organic double layer. According to the disclosure of this patent, the recording member consists of an electroconductive support material and a photoconductive layer of organic materials which contain a charge carrier producing dyestuff layer of a compound having an aromatic or heterocyclic polynuclear quinone ring system, and a transparent top layer of certain oxdiazoles. Apparently, this recording member is useful in electrophotographic copying processes where negative charging of the top layer occurs when an electron donor compound is selected for the member involved.
Many of the photoresponsive devices described, such as those disclosed in U.S. Pat. No. 4,265,990, include a transport layer, the function of which is to transport positive charges generated by the photogenerating layer. In a typical imaging sequence, these devices are charged negatively thus necessitating the need for a charge carrier transport material which will allow the migration of positive charges. Similar devices with electron transporting layers are relatively unknown except as disclosed herein particularly with reference to the copending application mentioned.
While photoresponsive imaging members with specific electron transporting layers are described in the referred to copending application which are suitable for their intended purposes, there continues to be a need for improved imaging members, particularly layered members comprised of novel electron transporting materials. Additionally, there continues to be a need for novel electron transporting materials which when selected for layered imaging devices allow the generation of acceptable images, and wherein these devices can be repeatedly used for many imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Moreover, there continues to be a need for improved layered imaging members with electron transporting substances, wherein the materials selected for the respective layers are substantially inert to users of such devices. Further, there continues to be a need for improved layered imaging members comprising electron transporting substances of sulfur incorporated dicyanomethylenefluorene carboxylates, and wherein the resulting imaging members can be positively charged enabling their use, for example, in xerographic color imaging processes with negatively charged toners. Furthermore, there is a need for electron transporting compounds which enable improved cycle-up and cycle-down characteristics when incorporated into photoconductive imaging members, and wherein the resulting members generate less undesirable ozone in comparison to those imaging members which are negatively charged. Additionally, there continues to be a need for positively charged layered photoresponsive imaging members with electron transporting compounds which are inert and safe to the operational users. Moreover, there continues to be a need for improved photoresponsive imaging members which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another enabling the continuous use of these members in repetitive imaging and printing systems, including color imaging systems.